The present invention relates to an optical element, an optical component having an anti-reflection function, and a master. Specifically, the present invention relates to an optical element in which structures are arranged at a pitch shorter than or equal to a wavelength of light in a use environment.
Conventionally, in an optical element that uses a light-transmissive substrate composed of glass, plastic, or the like, surface treatment is performed to suppress the surface reflection of light. A method in which a minute and dense uneven structure (moth-eye structure) is formed on the surface of the optical element is exemplified as the surface treatment (e.g., refer to refer to “Optical and Electro-Optical Engineering Contact” Vol. 43, No. 11 (2005), 630-637).
In general, in the case where a periodic uneven shape is formed on the surface of an optical element, diffraction is generated when light passes through the periodic uneven shape, which considerably reduces the amount of the light component of transmitted light that goes straight. However, when the pitch of the uneven shape is shorter than the wavelength of light transmitted, diffraction is not generated. For example, if the uneven shape is rectangular, an anti-reflection effect that is effective for single-wavelength light corresponding to the pitch, depth, or the like can be achieved.
Since the above-described optical element has good anti-reflection characteristics, it is expected that the optical element is applied to a solar cell and a display device. The following is proposed as the uneven structure in which anti-reflection characteristics are taken into account.
A minute tent-shaped uneven structure (pitch: about 300 nm, depth: about 400 nm) is proposed as a structure manufactured using electron-beam exposure (e.g., refer to NTT Advanced Technology Corporation, “Master Mold for Forming Anti-reflection (Moth-eye) Structure having no wavelength dependence”, [online], [accessed Sep. 1, 2008], Internet <http://keytech.ntt-at.co.jp/nano/prd—0033.html>).
Furthermore, a Super-RENS Technology Team, the Center for Applied Near-Field Optics Research of the Advanced Industrial Science and Technology has proposed a nano-hole structure with a diameter of 100 nm and a depth of 500 nm or more (e.g., refer to the National Institute of Advanced Industrial Science and Technology, “Development of Desktop Device Enabling Nanometer-scale Microfabrication”, [online], [accessed Sep. 1, 2008], Internet <http://aist.go.jp/aist_i/press_release/pr2006/pr20060306/pr20060306.html>). Such a structure can be formed by a microstructure formation method that uses an optical disc recording apparatus. Specifically, such a structure can be formed using a nanomachining device based on a thermal lithography technology in which a visible light laser lithography method using a semiconductor laser (wavelength 406 nm) is combined with a thermally nonlinear material (e.g., refer to non-Patent Document 3).
In addition, the inventors of the present invention have proposed a structure having a hanging bell shape or a truncated elliptic cone-like shape (e.g., refer to International Publication No. 08/023,816 Pamphlet). In this structure, anti-reflection characteristics close to those of a structure obtained by electron-beam exposure are achieved. Furthermore, the structure can be manufactured by a method in which a process for making a master of optical discs is combined with an etching process.